The finishing system of choice presently being used on the exterior of automobiles and trucks comprises a clear coating applied over pigmented base coating that is applied over a primer coating. The clear coating provides protection, in particular, protection from weathering, to the pigmented base coating and improves the appearance of the overall finish, in particular, provides improved gloss and distinctness of image. The primer coating provides adhesion to the substrate and, in particular, provides resistance to stone chipping. When used in refinishing of automobile and truck bodies, the clear coating and primer coating are required to have an acceptable “pot life” and reasonably short cure time period to allow for application of a subsequent coat and in the case of a clear coating to allow for further processing or handling of the vehicle without damaging the finish. The term “pot life” means the period of time after a coating is mixed with a crosslinking agent, with or without a catalyst, in which the composition remains at a sprayable viscosity.
The following U.S. Pat. Nos. 5,516,873, 5,126,170, 5,243,012, 5,236,741, 5,412,056, 5,580,945, and 6,005,062, show a variety of coating composition that contain polyaspartic acid derivatives but these compositions do not have a property balance of acceptable pot life and rapid curing time to form a sufficiently hard finish to allow additional handling and processing of a coated vehicle or work piece after the coating composition has been applied.
To improve the rate of curing EP 0939091 uses reactive amine compounds. A typical example of such an amine is the reaction product of 4,4′-methylenebiscyclohexanamine with two moles of diethyl maleate. However, coating compositions formulated with these reactive amines do not have the desired balance of acceptable pot-life and the desired cure rate after application to an object while maintaining or improving on the desired properties of the resulting finish. In an effort to improve pot life, solvents and catalysts have been used but solvents have a deleterious effect on VOC (volatile organic content) emissions, which is undesirable and catalysts can result in deterioration of film properties, such as durability. It is, therefore, desired to find a class of amine functional compounds for the reaction with isocyanates, which form coating compositions that overcome these problems and form acceptable finishes for automotive and truck substrates.
The novel composition of this invention utilizes amine and hydroxy amine functional compounds that form low VOC coating compositions having an optimum balance of pot life and curing time and form finishes, in particular, clear and primer finishes useful for automobiles and trucks. The clear coatings have excellent properties, such as hardness, gloss, low color, durability, weatherability, and in particular resistance to UV (ultraviolet light) degradation, particularly when reinforced with ultraviolet light absorbers and screeners and hindered amine light stabilizers. The primer coatings exhibit excellent adhesion to metal substrates, in particular, aluminum and steel substrates, and provide for excellent stone chip resistance.